Do Circulating Sex Hormones Influence Neuronal Susceptibility to Binge Alcohol?
Circulating sex-hormones influence various functions throughout the body, including neuroprotection and neurodegeneration across types of brain injury. Limited evidence exists to suggest whether sex hormones influence neuronal susceptibility to binge alcohol induced brain damage too. Stimulation of the stress response, microglial activation, and loss of neurons in the hippocampus are known outcomes of alcohol exposure. Alcohol injury is a stressor that results in neuroimmune activation and stimulates the hypothalamic-pituitary-adrenal-axis (HPA-axis) responsible for the body’s stress response. Sex hormones organize the HPA-axis during development, creating sex-based responses to stress, and are highly influential for activation of this axis throughout adulthood. Females produce a more robust response of cortisol (CORT) from the HPA than males under stressful conditions, this may be linked to increased risk of alcohol injury. Existing studies of gonad- (GDX) and ovariectomy (OVX) at adulthood report alterations in CORT secretion profiles, switching to patterns similar to the opposite intact sex. The removal of circulating estrogens may afford females protection from binge damage but males may lose their testosterone buffer, raising their response to alcohol. To study the relationship between circulating sex hormones and binge-induced brain damage, we performed GDX and OVX in adult rats. Quantification of neuron loss, neuroimmune response, and CORT levels were used to observe the influence of circulating sex hormones on binge alcohol-induced neuronal damage in males and females. We hypothesized binge exposure would produce greater neuron loss, more neuroimmune activation, and higher CORT levels in all binge groups compared to controls. We expected OVX females and intact males 3
to show similar damage profiles, and that GDX males and intact females would show similar damage profiles. Specifically, we expected higher CORT secretion in GDX males and intact females, compared to OVX females and intact males, accompanied by greater decrement in neurons and an increased neuroimmune response. Examination of the impact of removing circulating sex hormones did not support a role for circulating sex hormones in modulating the HPA-axis and CORT output. Binge exposure led to granule neuron loss in the hippocampus but no effect of removing circulating sex hormones was found in males or females. No effect of binge exposure or circulating sex hormones was found for the neuroimmune response in the hippocampus for either sex, but binge exposure and sex hormones influenced outcomes in the mPFC for males. Neuroimmune response, quantified by number of total, ramified, and activated microglia, was increased in the mPFC from binge exposure in sham males. GDX males showed a decrease in overall neuroimmune response, characterized by loss of ramified microglia, with exposure to binge alcohol. Our findings support the loss of granule neurons from binge exposure and an influence of circulating sex hormones on the mediation of the neuroimmune response to binge alcohol in males but not females.